cenotaph vs henge

cenotaph

noun
  • A monument, generally in the form of an empty tomb, erected to honour the dead whose bodies lie elsewhere, especially members of the armed forces who died in battle. 

henge

noun
  • A prehistoric enclosure in the form of a circle or circular arc defined by a raised circular bank and a circular ditch usually running inside the bank, with one or more entrances leading into the enclosed open space. 

How often have the words cenotaph and henge occurred in a corpus of books? (source: Google Ngram Viewer )